Field of the Invention
The present disclosure relates to an image forming apparatus, and more specifically relates to an image forming apparatus based on electrophotography.
Description of the Related Art
In an image forming apparatus based on electrophotography, means for electrically charging a photoconductor is known to include a non-contact charging system implemented by means of corona discharge or the like and a contact charging system implemented by means of a charging roller or the like. Recently, for the sake of energy saving or the like, the contact charging system has more widely been used relative to the non-contact charging system.
On the surface of the charging roller used for the contact charging system, a thin protective layer (surface layer) is mounted for the purpose of reducing adhesion of dirt or the like. The charging roller is generally positioned in contact with the photoconductor and configured to rotate following rotation of the photoconductor. Therefore, a stress applied from the photoconductor to the surface layer of the charging roller is caused to vary by repeated contact with and separation from the photoconductor. Due to the influence of this stress variation, the surface layer of the charging roller is gradually degraded to be eventually broken, resulting in generation of cracks.
As to the technique for detecting the surface state of the charging roller, Japanese Laid-Open Patent Publication No. 11-352754 discloses that light is applied to the charging roller and the light reflected from the charging roller is received to detect the surface property (surface roughness) of the charging roller. The technique disclosed in the above-referenced document changes AC current applied from a charging bias source to the charging roller, depending on information about the surface property of the charging roller, to thereby apply appropriate AC current to the charging roller, regardless of the state of the surface property of the charging roller.